1. Introduction
The present invention relates to a method and apparatus for sensing position particularly for use in land surveying and earth moving machinery control.
2. Field of the Invention
It is known to use rotating laser beams for position sensing. For example, U.K. patent application No. 2,152,320 (Siddall) describes a laser measurement system based on at least three rotating laser beams from two base stations which are separated by a known distance. A movable sensor to detect the beams and store the time at which the beams are detected is employed. A datum means is provided by a contra-rotating reference beam from at least one of the generators, and the time at which this reference beam is detected by the movable sensor is stored for comparison. As there are at least three rotating beams, they are rotated on separate, unique planes so that they can be differentiated.
U.K. patent application No. 2,089,615 (Tsumura) describes the use of one or more scanning laser beams in either a horizontal or a vertical plane for defining a path, which a vehicle fitted with a movable sensor is to follow. Position is determined solely with respect to the location on the movable sensor, at which the scanning beam is detected. Vertical position relative to a scanning beam in a horizontal plane may be determined, however, as the range of movement which can be detected is limited to the physical dimensions of the movable sensor, measurement of movement in a horizontal plane may not be measured outside of a pre-determined track, he width of which is determined by these physical dimensions.